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LONDON--(BUSINESS WIRE)-- FORM 8.3 PUBLIC OPENING POSITION DISCLOSURE/DEALING DISCLOSURE BY A PERSON WITH INTERESTS IN RELEVANT SECURITIES REPRESENTING 1% OR MORE Rule 8.3 of the Takeover Code (the Code) 1. KEY INFORMATION (a) Full name of discloser: Millennium International Management LP (b) Owner or controller of interests and short positions disclosed, if different from 1(a): The naming of nominee or vehicle companies is insufficient. For a trust, the trustee(s), settlor and beneficiaries must be named. (c) Name of offeror/offeree in relation to whose relevant securities this form relates: Use a separate form for each offeror/offeree Horizon Discovery Group plc (d) If an exempt fund manager connected with an offeror/offeree, state this and specify identity of offeror/offeree: (e) Date position held/dealing undertaken: For an opening position disclosure, state the latest practicable date prior to the disclosure 15th December 2020 (f) In addition to the company in 1(c) above, is the discloser making disclosures in respect of any other party to the offer? If it is a cash offer or possible cash offer, state N/A No 2. POSITIONS OF THE PERSON MAKING THE DISCLOSURE If there are positions or rights to subscribe to disclose in more than one class of relevant securities of the offeror or offeree named in 1(c), copy table 2(a) or (b) (as appropriate) for each additional class of relevant security. (a) Interests and short positions in the relevant securities of the offeror or offeree to which the disclosure relates following the dealing (if any) Class of relevant security: 1p ordinary (GB00BK8FL363) Interests Short positions Number % Number % (1) Relevant securities owned and/or controlled: - - - - (2) Cash-settled derivatives: 5,644,624 3.564% - - (3) Stock-settled derivatives (including options) and agreements to purchase/sell: - - - - TOTAL: 5,644,624 3.564% - - All interests and all short positions should be disclosed. Details of any open stock-settled derivative positions (including traded options), or agreements to purchase or sell relevant securities, should be given on a Supplemental Form 8 (Open Positions). (b) Rights to subscribe for new securities (including directors and other employee options) Class of relevant security in relation to which subscription right exists: Details, including nature of the rights concerned and relevant percentages: 3. DEALINGS (IF ANY) BY THE PERSON MAKING THE DISCLOSURE Where there have been dealings in more than one class of relevant securities of the offeror or offeree named in 1(c), copy table 3(a), (b), (c) or (d) (as appropriate) for each additional class of relevant security dealt in. The currency of all prices and other monetary amounts should be stated. (a) Purchases and sales Class of relevant security Purchase/sale Number of securities Price per unit (b) Cash-settled derivative transactions Class of relevant security Product description e.g. CFD Nature of dealing e.g. opening/closing a long/short position, increasing/reducing a long/short position Number of reference securities Price per unit (GBP) GB00BK8FL363 Equity Swap Increasing a long position 1,345 1.85 GB00BK8FL363 Equity Swap Reducing a long position 205 1.85 (c) Stock-settled derivative transactions (including options) (i) Writing, selling, purchasing or varying Class of relevant security Product description e.g. call option Writing, purchasing, selling, varying etc. Number of securities to which option relates Exercise price per unit Type e.g. American, European etc. Expiry date Option money paid/ received per unit (ii) Exercise Class of relevant security Product description e.g. call option Exercising/ exercised against Number of securities Exercise price per unit (d) Other dealings (including subscribing for new securities) Class of relevant security Nature of dealing e.g. subscription, conversion Details Price per unit (if applicable) 4. OTHER INFORMATION (a) Indemnity and other dealing arrangements Details of any indemnity or option arrangement, or any agreement or understanding, formal or informal, relating to relevant securities which may be an inducement to deal or refrain from dealing entered into by the person making the disclosure and any party to the offer or any person acting in concert with a party to the offer: Irrevocable commitments and letters of intent should not be included. If there are no such agreements, arrangements or understandings, state none NONE (b) Agreements, arrangements or understandings relating to options or derivatives Details of any agreement, arrangement or understanding, formal or informal, between the person making the disclosure and any other person relating to: (i) the voting rights of any relevant securities under any option; or (ii) the voting rights or future acquisition or disposal of any relevant securities to which any derivative is referenced: If there are no such agreements, arrangements or understandings, state none NONE (c) Attachments Is a Supplemental Form 8 (Open Positions) attached? NO Date of disclosure: 16th December 2020 Contact name: Milos Naumovic Telephone number: +44 203 650 8203 Public disclosures under Rule 8 of the Code must be made to a Regulatory Information Service and must also be emailed to the Takeover Panel at monitoring@disclosure.org.uk. The Panels Market Surveillance Unit is available for consultation in relation to the Codes disclosure requirements on +44 (0)20 7638 0129. The Code can be viewed on the Panels website at www.thetakeoverpanel.org.uk.

Answer: Form 8.3 - Horizon Discovery Group plc