If the following had been his marriage, surely it would have got into Burke’s Peerage?  Meantime, I simply don’t know, short of buying the marriage cert (which will give his second name and his father’s name):

Name: TENNANT, Edward T
Registration District: Northumberland North Second
County: Northumberland
Year of Registration: 2000
Month of Registration: November
Spouse's last name: Bridgeman
District No: 679
Page No: 0420
Ent No: 011
Source Code: A11

There are no Edward T Tennant marriages in Scotland from 1887 to 2006.
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