to be designed or designed

[azkad]

DEAR MODERATORS, please, help me with the extract below. In my opinion, to be designed means designed, and was to become means became, but what is the difference? How do we differentiate between to be designed and designed?

The Queluz National Palace is a Portuguese 18th-century palace located at Queluz, a freguesia of the modern-day Sintra municipality, in the District of Lisbon. One of the last great Rococo buildings to be designed in Europe, the palace was conceived as a summer retreat for Dom Pedro of Braganza, who was later to become husband and then king consort to his own niece, Queen Maria I.

[Tdol]

In the first case, there is no real difference- your version is just a shortening. In the second case, your version works, but the use of 'was ... to become' `could imply that this was an unexpected result.