Conversation so far:
What is the name of Karlheinz Stockhausen's wife ?
Doris Andreae (m. 1951; div. 1965) and Mary Bauermeister (m. 1967; div. 1972)
When was Karlheinz Stockhausen married to Doris Andreae ?
On 29 December 1951, in Hamburg, Karlheinz Stockhausen married Doris Andreae.
How many children did Karlheinz Stockhausen and Doris Andreae have together ?
Together they had four children: Suja (b. 1953), Christel (b. 1956), Markus (b. 1957), and Majella (b. 1961)
Did Karlheinz Stockhausen have any other wives besides Doris Andreae?
Karlheinz Stockhausen married Mary Bauermeister.

Question: When did he marry Mary Bauermeister ?
Self-contained rewrite: When did Karlheinz Stockhausen marry Mary Bauermeister ?