German mathematician, being endlessly awkward, interrupts old queen (7)
I believe the answer is:
leibniz
'german mathematician' is the definition.
(I know that Leibniz is a mathematician)
'being endlessly awkward interrupts old queen' is the wordplay.
'endlessly' means to remove the last letter.
'awkward' indicates an anagram.
'interrupts' means one lot of letters goes inside another.
'old queen' becomes 'liz' (Queen Elizabeth).
'being' with its final letter taken away is 'bein'.
'bein' with letters rearranged gives 'eibn'.
'eibn' placed within 'liz' is 'LEIBNIZ'.
(Other definitions for leibniz that I've seen before include "German polymath" , "Philosopher" .)