Conversation so far:
What year was the Sweet's record deal?
The Sweet made its debut at the Pavilion in Hemel Hempstead on 9 March 1968 and soon developed a following, which led to a contract with Fontana Records.
What was the Sweet's new lineup?
Guitarist Mick Stewart joined in 1969.

Question: What happened after he joined?
Self-contained rewrite: What happened after Mick Stewart joined the Sweet?